The purpose of this research plan is to study the development of binocular vision in normal human infants and young children, and to apply the normative data to the study of patients with strabismus. A major thrust of this research is the development of a paradigm to study vision via the recording of eye movements. Our ultimate goal is to detect and treat abnormalities of binoculr vision, and to reduce the need for additional surgery in strabismic patients. Evidence is accumulating that binocular vision is not a single entity but rather is a number of separate, but interrelated, mechanisms. We plan to evaluate binocular vision by use of three tests designed to measure different binocular functions: summation (facilitation), stereopsis (cooperation) and rivalry (inhibition). Binocular summation is defined as the greater amplitude of the visual evoked response (VER) with binocular stimulation compared to monocular stimulation. We plan to measure binocular summation by recording VERs with pattern stimulation. Stereopsis, depth perception from binocular disparity, will be measured by a novel technique that combines the measurement of eye movements to a moving stimulus contained in a dynamic random element stereogram. Binocular rivalry, which involves alternating inhibition between the eyes, will be elicited by vertical gratings moving in opposite (temporal-to-nasal) direction in each eye. The optokinetic nystagmus generated by the moving gratings will indicate the dominant direction of movement, and dominant eye, at any given time during binocular rivalry. Once normative data is obtained, two groups of strabismic patients (early-onset and acquired esotropes) will be tested before and after strabismus surgery. Data from normal infants and young children will determine the relation among the three binocular functions and how each develops with age. Measurement of each binocular function in early-onset and acquired esotropes before surgery would allow us to document the decrements in binocular function that occur with strabismus. Measurement of the binocular functions at various times after surgery would enable us to follow the progress and development of binocular vision and to detect binocular abnormalities which may precede a return of esotropia. Once the premeditating factors for a return of esotropia are known, clinical intervention could be instituted to prevent a return of esotropia and thus reduce the need for additional surgery.